exec: Rename target_words_bigendian() -> target_big_endian()

In commit 98ed8ecfc9 ("exec: introduce target_words_bigendian()
helper") target_words_bigendian() was matching the definition it
was depending on (TARGET_WORDS_BIGENDIAN). Later in commit
ee3eb3a7ce ("Replace TARGET_WORDS_BIGENDIAN") the definition was
renamed as TARGET_BIG_ENDIAN but we didn't update the helper.
Do it now mechanically using:

  $ sed -i -e s/target_words_bigendian/target_big_endian/g \
        $(git grep -wl target_words_bigendian)

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20250417210025.68322-1-philmd@linaro.org>

cpu-target.c

@@ -160,8 +160,8 @@ void cpu_abort(CPUState *cpu, const char *fmt, ...)
     abort();
 }
 
-#undef target_words_bigendian
-bool target_words_bigendian(void)
+#undef target_big_endian
+bool target_big_endian(void)
 {
     return TARGET_BIG_ENDIAN;
 }